In recent years, it is known even in surgical fields that humoral factors produced at excessive levels play important roles in formation of pathological conditions during the perioperative period of significantly invasive surgery or the acute phase of a medical emergency such as an infectious disease. It is extremely important to measure various humoral factors in order to gain early, comprehensive knowledge of a pathology that changes every day or every second under such invasion and to apply the understanding clinically. Studies concerning various humoral factors in the process of shifts from sepsis to multiple organ dysfunction syndrome (MODS, by which the functions of a plurality of organs are damaged) have drastically progressed together with the development of molecular biological techniques. Recent studies on MODS have been improved to indicate a study approach that involves analyzing the mechanism of damage at the cellular level and microenvironment or humoral factors, so as to get closer to the pathology. Specifically, based on the understanding that MODS cases are extremely analogous to each other in terms of onset mechanism or pathology even if the causes of MODS cases differ (e.g., an MODS case due to sepsis), the control of factors involved in the shift to pathology that is developed much earlier before the onset of MODS has recently been emphasized. It can be said that clinicians and researchers are currently focusing on elucidation of the pathology of sepsis that occurs at the prestage of MODS and establishment of effective countermeasures against the pathology rather on treatment for MODS itself.
Humoral factors are useful as inflammatory markers. Specifically, CRP (C-reactive protein), TNF-α, IL-1, IL-6, IL-8, IL-10, MIP-1, HMGB-1, MIF, C5a, calcitonin, and the like are known (Marshall et al., Crit Care Med 31: 1560, 2003). It has been reported concerning CRP such that CRP is used in combination with the number of platelets or the like for evaluation of the prognosis of severe sepsis (Asayama et al., Keio J Med 47: 19 1998). It has also been reported that no significant differences are confirmed between sepsis and trauma (Endo et al., Journal of Infection 73: 197 1999). Hence, solid evaluation has not been established for CRP. Similarly, in the case of TNF-α or IL-6, while it has been reported that no significant differences have been confirmed between sepsis and trauma (Endo et al., Journal of Infection 73: 197 1999), it has also been reported that IL-6 is used as a prognosis marker for sepsis (Reinhart et al., Crit Care Med 29: 765, 2001). Thus, solid evaluation has not been established for TNF-α or IL-6. Moreover, it has been reported that IL-10 is effective (Ono et al., Am J Surg 188: 150, 2004), however, it cannot be said that the effects of IL-10 have been sufficiently verified through use. Involvement of MIF in acute respiratory distress syndrome (ARSD), bronchial asthma, or the like has been reported (Donnelly et al., Nat Med 3: 320, 1997; Rossi et al., J Clin Invest 101: 2869, 1998), but it is unknown whether or not MIF can be used as a marker. It has not been revealed if the above-mentioned humoral factors cause sepsis or are produced as a result of sepsis.
Inflammatory reactions are biological reactions that limit the spreading of damage to a living body due to invasion and repair such damage. They occur as nonspecific reactions against all injuries or invasions. Inflammatory reactions are actually physiological biological reactions that take place in close association with neuroendocrine reactions, immunoinflammatory reactions, and coagulation-fibrolysis reactions. Inflammatory reactions are expressed locally in the forms of flare, swelling, pain, heat, and the like, and they cause systemic reactions with fever, tachycardia, tachypnea, and increased number of leukocytes when invasion is significant. Such conditions are referred to as systemic inflammatory response syndrome (SIRS). Examples thereof include SIRS not associated with infection or the like, but rather with trauma, burn, pancreatitis, and states after significantly invasive surgery, as well as SIRS associated with infection due to bacteria, fungi, parasites, viruses, or the like. In particular, SIRS caused by infection is referred to as sepsis.
Inflammatory reactions are established by vasodilation, vascular hyperpermeability, leukocyte-vascular endothelial cell activation, or the like. These reactions are induced by complements, amine, kinin, prostanoid, cytokine, and thrombin that are nonspecifically produced as invasion proceeds. Localized inflammatory reactions are induced by local noxious stimuli. However, when biological invasion is significant, systemic escape of these inflammatory mediators (and in particular, cytokine and thrombin) takes place and then systemic vasodilation, hyperpermeability, and leukocyte-vascular endothelial cell activation are observed. Inflammatory reaction has stages of receipt of noxious stimuli, reaction, and repairment. When a systemic inflammatory reaction is sustained, the reaction does not reach the repairment stage, so that biological homeostasis fails. In such case, it is known that MODS is induced to lead the living body to death.
For defense against invasion in the living body, three systems, the nervous system, the endocrine system, and the immune system, undergo reactions while closely interacting with each other. The nervous and endocrine systems are activated as invasion proceeds, resulting in enhanced energy metabolism, gluconeogenesis, increased cardiac output, and the like. Thus, inflammatory reactions are systemically enhanced. Meanwhile, cortisol is known to suppress the immune system and catecholamine is known to suppress the activity of NK cells or killer T cells, which are immunocytes. Bacterial infection or the occurrence of tissue damage activates the complement system or the blood coagulation system, along with which vascular endothelial cells are activated and phagocytic cells including monocytes, macrophages, and neutrophils migrate. Thus, inflammatory cytokines (composed mainly of TNF-α and IL-1) are freed from the damaged sites. With liberation of these inflammatory cytokines, protease or active oxygen, platelet-activating factors, and the like are also freed, forming the pathology of SIRS. Therefore, it is possible to consider that SIRS is also a pathological condition caused by hypercytokinemia (Riedemann et al., Nat Med 9: 517, 2003).
It has been reported that in the U.S. that about 750,000 persons are affected with sepsis yearly and 210,000 or more persons lose their lives due to sepsis (Wheeler et al., N Engl J Med 340: 207, 1999; Severansky et al., Sepsis 3: 11, 1999; Hotchkiss et al., N Engl J Med 348: 138, 2003). Furthermore, treatment for sepsis causes significant economic impact because of lengthy ICU hospital stays or increased amounts of resources used. However, although establishment of a therapeutic method against sepsis that is also referred to as high inflammatory cytokinemia has been attempted as an emergent issue throughout the world, no therapeutic method currently exists by which reduction of sepsis fatalities can be realized (Vincent et al., Clin Infect Dis 34: 1084, 2002). A therapeutic method has been reported recently by which significant improvement in the prognosis of severe sepsis can be achieved via administration of activated protein C (APC) (Bernard et al., N Engl J Med 344: 699, 2001). APC will be approved by the U.S. Food and Drug Administration (FDA) for the first time as a therapeutic agent against severe sepsis. However, the degree of effectiveness of APC is a slight rise in lifesaving rate of only approximately 6%-7%. Thus, sepsis is still considered to be a pathological condition with a very high fatality rate that is extremely difficult to cure. Furthermore, activated protein C is an endogenous protein that activates not only coagulation-suppressing functions, but also fibrinolytic functions, thereby inhibiting thrombus formation or inflammation (DePalo et al., Advances in Sepsis 1: 114, 2001). In addition to the palliative effects of activated protein C, it is inferred that APC increases the risk of bleeding because of its features. In particular, intracranial hemorrhage is a severe adverse event. Thus, administration of APC necessitates sufficient care so that APC is administered in compliance with contraindicated conditions. Attempts that have been made other than the aforementioned attempts are as shown below.                (1) Large amounts of steroids: Application of large amounts of steroids has succeeded as a pretreatment for animals with endotoxemia or bacillaemia. Based on such successes, the effects of administration of large amounts of steroids to patients with septic shock have been examined in early clinical tests. However, in large-scale double-blind studies, validity has never been reported even in cases of administration of steroids during early development of septic shock (Meduri et al., Sepsis 3: 21, 1999; Bernard et al., N Engl J Med 317: 1565, 1987; Bone et al., Chest 92: 1032, 1987).        (2) Antiendotoxin antibody: Treatment with a specific antiendotoxin antibody has been examined using polyclonal human immunoglobulin G against heat-sterilized E. coli J5, mouse (E5) and humanized (HA1A) monoclonal antibodies against endotoxin lipid A, and the like. Patients with severe gram-negative bacterial infectious disease have been examined as subjects (Llewelyn et al., Sepsis 3: 39, 1999). Validity has never been confirmed in large-scale tests.        (3) Anti-TNF treatment: Anti-TNF treatment is neutralization therapy targeting TNF-α (inflammatory cytokine), which uses an anti-TNF monoclonal antibody and a soluble TNF receptor. It has been reported that survival prospects can be improved in many sepsis models via suppression of the effects of TNF-α (Tracey et al., Nature 330: 662, 1987; Pennington et al., Clin Infect Dis 17 (Suppl 2): S515, 1993). Although a plurality of phase II and phase III clinical tests have been conducted, it has never been reported that survival rates have been improved by suppressing the effects of TNF-α with the use of anti-TNF treatment (Abraham et al., JAMA 273: 934, 1995; Reinhart et al., Crit Care Med 24: 733, 1996; Severansky et al., Sepsis 3: 11, 1999; Reinhart et al., Crit Care Med 29: S121, 2001).        (4) IL-1 receptor antagonist (IL-IRa): IL-1 is also an inflammatory cytokine, but is known to induce many pathological conditions of sepsis (Ohlsson et al., Nature 348: 550 1990). Such effects can be suppressed with the use of IL-IRa, which is a natural IL-1 receptor antagonistic substance. However, a lack of differences between a treatment group (group of treated patients) and a placebo group in terms of survival rate has been demonstrated by three tests (two double-blind tests) conducted for severe sepsis patients (Fisher et al., JAMA 271: 1836, 1994; Opal et al., Crit Care Med 25: 1115, 1997; Severansky et al., Sepsis 3: 11, 1999).        (5) PAF receptor antagonist (PAFra): Platelet agglutinating factor (PAF) is a phospholipid involved in cytokine release during sepsis. It has been demonstrated by two double-blind tests that PAF receptor antagonist (BN52021) does not significantly improve survival (Dhainaut et al., Crit Care Med 22: 1720, 1994; Dhainaut et al., Crit Care Med 26: 1963, 1998; Severansky et al., Sepsis 3: 11, 1999). It has been recently demonstrated again by a phase II clinical test using another compound (BB-882) that the compound does not significantly improve the survival of severe sepsis patients.        (6) Nonsteroidal anti-inflammatory drug: an antiprostaglandin drug, Ibuprofen, has been examined in three double-blind tests, but the usefulness of Ibuprofen has never been demonstrated in any of these cases (Bernard et al., N Engl J Med 336: 912, 1997; Severansky et al., Sepsis 3: 11, 1999).        (7) Bradykinin antagonist: Bradykinin is a bioactive peptide involved in cytokine release and changes in blood vessels during sepsis. Improvement in lethality with the use of a bradykinin antagonist has never been observed in two double-blind tests (Fein et al., JAMA 277: 482, 1997; Severansky et al., Sepsis 3: 11, 1999).        
As described above, although various therapeutic methods for sepsis have been advanced, suppression of the incidence rate has never been confirmed. Sepsis is still a disease for which reduction in the number of deaths therefrom has been impossible to achieve. Novel exploitation of preventive methods or therapeutic methods for sepsis are required.
RANKL, which is a ligand of RANK, is an osteoclastic differentiation-inducing factor and is known to induce osteoclasts from precursor cells of the macrophage system under coexistence with a macrophage colony-stimulating factor (M-CSF) (see Yasuda et al., Proc Natl Acad Sci USA 95: 3597, 1998 and Lacey et al., Cell 93: 165, 1998). Specifically, RANKL is produced by osteoblasts and binds to RANK on precursor cells of the macrophage system, so as to induce the cells to become osteoclasts. Furthermore, at this time, OPG (osteoprotegerin) structurally analogous to RANK suppresses the effects of RANKL, as a decoy receptor. In this manner, bone metabolism is controlled by balancing RANKL and OPG amounts. RANKL is a membrane-associated protein and a part thereof is present in blood in a soluble form. Some bone metabolism diseases confirmed with variation in the concentration of soluble RANKL (sRANKL) have been reported. The usefulness of RANKL as a bone metabolism marker has been suggested, and medical applications of RANKL have been examined (see Rogers et al., J Clin Endoceinol Metab 90: 6323, 2005 and see JP Patent Publication (Kohyo) No. 2004-526748 A; JP Patent Publication (Kohyo) No. 2002-509430 A; and International Publication WO98/46644). Moreover, discussion often takes place concerning RANKL based on the concentration ratio of soluble RANKL to OPG; that is, the ratio of the concentration of soluble RANKL to OPG. As described above, the role of RANKL in the bone metabolism system has been conventionally known; however, the functions of RANKL in the natural immune system have remained unclear and the biological meaning of soluble RANKL existing in blood has also remained unclear.